Signed for £27 million from Southampton in July, Shaw quickly faced criticism over his fitness levels from manager Louis Van Gaal, who ordered the 19-year-old to train on his own during the club's pre-season tour of America.

"Luke needs to be fit, and he's not very fit and can't perform how I want. He needs to be fit and to train individually," Van Gaal said at the time. "I can't judge why. I see what I see."

With no other recognised senior left-back at the club following Patrice Evra's move to Juventus, Shaw's injury could see United step up their pursuit for new defensive recruits.

Meanwhile, Ajax's Daley Blind, who starred for Van Gaal's Netherlands in Brazil at left-back and centre-back, appears keen to follow his former international manager to United.

The injuries are piling up as United prepare to kick off their Premier League campaign against Swansea on Saturday. In addition to the loss of Shaw, Van Gaal is concerned he will be without central defender Jonny Evans and wing-back Antonio Valencia, who also missed Tuesday's game.

"We have a lot of injuries now," Van Gaal said after the match. "Evans was injured, Shaw was injured, Valencia was injured and they are three defenders so we have to wait and see if they can play on Saturday."

Van Gaal also said Marouane Fellaini and Adnan Januzaj, who both came off the bench against Valencia, are not yet fit enough to play more than 15 minutes following their World Cup exertions with Belgium.

"Fellaini and Januzaj have only [had] one week, one-and-a half weeks to train with us so they cannot make more minutes," Van Gaal said.